The invention relates to a power supply circuit for generating a first direct voltage on a first lead and a second direct voltage on a second lead, said second voltage being lower than the first voltage, a preload arranged between the first lead and a reference potential having a tap which is coupled to the second lead.
A circuit of this type is known from German Patent Specification No. 3,318,503. In this known circuit, the preload comprises the series arrangement of a plurality of ohmic resistors having a high value. The first voltage is an extra high tension (E.H.T.) for a final anode of a picture display tube. A current which is a loss always flows through the preload, which is why it is generally termed "bleeder" in the English language. This current ensures that the E.H.T. generator always has a load so that the E.H.T. cannot increase too high in the absence of beam current, which could cause X-ray radiation and that the internal impedance of the E.H.T. source is somewhat reduced.
For the focussing electrode of the picture display tube, the second voltage is derived from a suitable tap on the bleeder. In this way, a separate generation of the second voltage, for example with a separate transformer is not necessary. A drawback is, however, that the two voltages may influence each other in the case of variations of their loads, in this case the focussing current and the beam current. In fact, the use of an ohmic load resistor having a practical real value leads to an inadmissibly high internal impedance of the voltage source which is derived therefrom.